Why do doctors use colonoscopy?

Doctors also use colonoscopy as a screening tool for colon polyps and cancer. Screening is testing for diseases when you have no symptoms. Screening may find diseases at an early stage, when a doctor has a better chance of curing the disease.

Screening for Colon and Rectal Cancer

Your doctor will recommend screening for colon and rectal cancer —also called colorectal cancer—starting at age 50 if you don’t have health problems or risk factors that make you more likely to develop colon cancer.1

If you are more likely to develop colorectal cancer, your doctor may recommend screening at a younger age, and more often.

If you are older than age 75, talk with your doctor about whether you should be screened. For more information, read the current colorectal cancer screening guidelines from the U.S. Preventive Services Task Force (USPSTF).

Government health insurance plans, such as Medicare, and private insurance plans sometimes change whether and how often they pay for cancer screening tests. Check with your insurance plan to find out how often your plan will cover a screening colonoscopy.

How do I prepare for a colonoscopy?

To prepare for a colonoscopy, you will need to talk with your doctor, change your diet for a few days, clean out your bowel, and arrange for a ride home after the procedure.

Talk with your doctor

You should talk with your doctor about any health problems you have and all prescribed and over-the-counter medicines, vitamins, and supplements you take, including

Change your diet and clean out your bowel

A health care professional will give you written bowel prep instructions to follow at home before the procedure so that little or no stool remains in your intestine. A complete bowel prep lets you pass stool that is clear and liquid. Stool inside your intestine can prevent your doctor from clearly seeing the lining.

You may need to follow a clear liquid diet for 1 to 3 days before the procedure. You should avoid red and purple-colored drinks or gelatin. The instructions will include details about when to start and stop the clear liquid diet. In most cases, you may drink or eat the following:

fat-free bouillon or broth

gelatin in flavors such as lemon, lime, or orange

plain coffee or tea, without cream or milk

sports drinks in flavors such as lemon, lime, or orange

strained fruit juice, such as apple or white grape—avoid orange juice

water

Different bowel preps may contain different combinations of laxatives—pills that you swallow or powders that you dissolve in water or clear liquids. Some people will need to drink a large amount, often a gallon, of liquid laxative over a scheduled amount of time—most often the night before and the morning of the procedure. Your doctor may also prescribe an enema.

The bowel prep will cause diarrhea, so you should stay close to a bathroom. You may find this part of the bowel prep hard; however, finishing the prep is very important. Call a health care professional if you have side effects that keep you from finishing the prep.

Your doctor will tell you how long before the procedure you should have nothing by mouth.

The instructions will include details
about when to start and stop the clear liquid diet.

Arrange for a ride home

For safety reasons, you can’t drive for 24 hours after the procedure, as the sedatives or anesthesia need time to wear off. You will need to make plans for getting a ride home after the procedure.

How do doctors perform a colonoscopy?

A doctor performs a colonoscopy in a hospital or an outpatient center. A colonoscopy usually takes 30 to 60 minutes.

A health care professional will place an intravenous (IV) needle in a vein in your arm or hand to give you sedatives, anesthesia, or pain medicine, so you won’t be aware or feel pain during the procedure. The health care staff will check your vital signs and keep you as comfortable as possible.

For the procedure, you’ll lie on a table while the doctor inserts a colonoscope through your anus and into your rectum and colon. The scope inflates your large intestine with air for a better view. The camera sends a video image to a monitor, allowing the doctor to examine your large intestine.

The doctor may move you several times on the table to adjust the scope for better viewing. Once the scope reaches the opening to your small intestine, the doctor slowly removes the scope and examines the lining of your large intestine again.

For the procedure, you will lie on a table while the doctor
inserts a colonoscope through your anus and into your rectum and colon.

During the procedure, the doctor may remove polyps and will send them to a lab for testing. You will not feel the polyp removal. Colon polyps are common in adults and are harmless in most cases. However, most colon cancer begins as a polyp, so removing polyps early helps to prevent cancer.

If your doctor finds abnormal tissue, he or she may perform a biopsy. You won’t feel the biopsy.

What should I expect after a colonoscopy?

After a colonoscopy, you can expect the following:

The anesthesia takes time to wear off completely. You’ll stay at the hospital or outpatient center for 1 to 2 hours after the procedure.

You may feel cramping in your abdomen or bloating during the first hour after the procedure.

After the procedure, you—or a friend or family member—will receive instructions on how to care for yourself after the procedure. You should follow all instructions.

You’ll need your pre-arranged ride home, since you won’t be able to drive after the procedure.

You should expect a full recovery and return to your normal diet by the next day.

After the sedatives or anesthesia wear off, your doctor may share what was found during the procedure with you or, if you choose, with a friend or family member.

If the doctor removed polyps or performed a biopsy, you may have light bleeding from your anus. This bleeding is normal. A pathologist will examine the biopsy tissue, and results take a few days or longer to come back. A health care professional will call you or schedule an appointment to go over the results.

After the procedure, you—or a friend or family member—will receive instructions
on how to care for yourself after the procedure. You should follow all instructions.

What are the risks of colonoscopy?

A study of screening colonoscopies found roughly 4 to 8 serious complications for every 10,000 procedures.3

Bleeding and perforation are the most common complications from colonoscopy. Most cases of bleeding occur in patients who have polyps removed. The doctor can treat bleeding that happens during the colonoscopy right away.

You may have delayed bleeding up to 2 weeks after the procedure. The doctor can diagnose and treat delayed bleeding with a repeat colonoscopy. The doctor may need to treat perforation with surgery.

Seek Care Right Away

If you have any of the following symptoms after a colonoscopy, seek medical care right away:

This content is provided as a service of the National Institute of Diabetes and Digestive and Kidney Diseases
(NIDDK), part of the National Institutes of Health. The NIDDK translates and disseminates research findings
through its clearinghouses and education programs to increase knowledge and understanding about health and
disease among patients, health professionals, and the public. Content produced by the NIDDK is carefully
reviewed by NIDDK scientists and other experts.

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